rollup.rb treats # parameter-expansion operators as comments

[memotype]

Severity: Medium
Expected real-world likelihood: Medium for future maintenance; none in the current source

Problem

rollup.rb removes text from any unprotected # through the end of the line. Valid Bash parameter expansions use the same character for length and prefix removal, so adding an ordinary construct such as ${#array[@]} or ${value#prefix} to the readable source can silently corrupt generated scripts.

The current bj.sh does not contain an affected core construct, and current generated files reproduce byte-for-byte. This is a guardrail issue for future compact parser work rather than a current runtime regression.

Reproduction

printf '%s\n' 'x=${#a[@]}' 'y=${value#prefix}' | ./rollup.rb

Actual compact code after the copyright header:

x=${y=${value

The source lines are valid Bash but are truncated at each #.

Suspected cause

The transformation list includes:

[/#.*\n/, '']

Quoted string literals are protected before transformations, but unquoted parameter expansions are not.

Possible fixes (suggestions only)

These are possible approaches, not prescribed implementations:

• Protect the small set of Bash parameter-expansion forms containing # before comment stripping and restore them afterward.
• Narrow comment recognition so # inside a parameter expansion is not treated as a comment.
• Add focused generator fixtures for the supported compact Bash constructs.

The solution should remain small and auditable; this issue does not suggest turning rollup.rb or linebreak.rb into a general Bash parser.

Suggested regression coverage

• ${#name} and ${#array[@]};
• ${value#prefix} and ${value##prefix};
• real inline comments still being removed;
• hashes inside single- and double-quoted strings remaining unchanged;
• generated output passing bash -n;
• current bj.sh still regenerating byte-for-byte.